Abstract: A chopper wheel assembly includes a collimator configured to narrow an x-ray beam, a chopper wheel has a planar surface configured to face in a direction of the collimator and a housing configured to receive the chopper wheel. The chopper wheel includes a central axis, a plurality of slits in the planar surface, a first projection extending from the planar surface in a direction of the collimator and a second projection extending from the planar surface in the direction of the collimator. The slits extend in radially-outward direction relative to the central axis. The first projection is located radially outward of the plurality of slits and the second projection is located radially inward of the plurality of slits. Each projection is provided for 360 degrees about the central axis. The housing includes an interior wall including a first groove configured to receive the first projection and a second groove configured to receive the second projection with the chopper wheel received within the housing.